Contact angle of water on a model heterogeneous surface. A density functional approach

TL;DR

This study employs a density functional approach to analyze how pre-adsorbed heterogeneous layers on a surface influence the water contact angle, revealing complex effects on wetting behavior and phase densities.

Contribution

It introduces a model for heterogeneous surfaces with pre-adsorbed layers, exploring their impact on water contact angles and phase densities using a density functional framework.

Findings

Pre-adsorbed obstacles increase wetting temperature non-linearly.

Attractive pre-adsorbed species can cause maximum contact angle dependence.

Pre-adsorbed layers significantly alter local phase densities.

Abstract

We use a density functional approach to calculate the contact angle of the water model on a heterogeneous, graphite-like surface. The surface heterogeneity results from the pre-adsorption of a layer of spherical species. The pre-adsorbed molecules can also be a mixture of molecules of different sizes. The presence of pre-adsorbed layer causes geometrical and energetical heterogeneity of the surfaces. Two cases are considered. The pre-adsorbed molecules can either behave like hard-sphere obstacles, or they can also attract the molecules of water. In the first case, an increase of the amount of pre-adsorbed species leads to an increase of the wetting temperature, but this increase does not depend linearly on the amount of obstacles. In the case of obstacles exerting attractive forces on water molecules, the curves describing the dependence between the amount of pre-adsorbed species and the contact angle can exhibit a maximum. In addition, we have also studied how the pre-adsorbed species influence the local densities of gaseous and liquid phases in contact with a modified solid surface.